The present invention relates in general to passive entry systems for passenger vehicles, and, more specifically, to an electronic module for passive entry systems that is easily customized to function correctly in any particular model of vehicle despite differences in vehicle dimensions, antenna locations, and presence of signal attenuating structures.
It is well known in the automotive industry to provide for remote vehicle access, such as through the use of remote keyless entry (RKE) systems. RKE systems may be characterized as active or passive in nature. In an active system, a switch or pushbutton on a remote transmitter must be activated by an operator in order to have a desired remote function performed, such as locking or unlocking the vehicle doors. In contrast, a passive entry system does not require a pushbutton activation by an operator in order to have a desired remote function performed.
In passive entry systems, a remote transceiver is provided which is commonly referred to as a “fob” or a “card.” Such a fob or card may be attached to a key chain as a separate unit, or may be part of the head of an ignition key. The fob or card automatically transmits radio frequency (RF) signals to a vehicle in order to perform any of a variety of remote vehicle functions, such as unlocking a vehicle door, enabling the vehicle engine, and/or activating internal and/or external vehicle lights.
Passive entry systems include a transceiver in an electronic control module installed in the vehicle. The vehicle transceiver and/or control module is provided in communication with various vehicle devices in order to perform a variety of functions. For example, the vehicle transceiver and/or control module may be provided in communication with a door lock mechanism in order to unlock a vehicle door in response to an unlock request, or may be provided in communication with the vehicle engine in order to start the engine in response to an engine start request.
A sensor or switch may be provided in a vehicle door handle in order to provide the unlock request. More particularly, when the vehicle owner makes physical contact with the door handle, such as by grasping or pulling the handle, such a sensor provides the vehicle transceiver and/or control module with an indication of such contact. After receiving such an indication, the vehicle transceiver and/or control module automatically transmits a passive entry challenge signal. Upon receipt of the challenge signal, the remote transceiver fob or card carried by the user determines if the challenge signal is valid and, if so, automatically transmits a response which includes a unique identification code of the fob. The vehicle transceiver and/or control module compares the identification code with the codes of authorized fobs and if a match is found then the control module generates a control signal that is transmitted to the door lock mechanism for use in unlocking the vehicle door.
In performing passive entry functions, it is often necessary to localize (i.e., determine the location of) the user carrying the fob in deciding whether a particular passive entry function should be performed. For example, when the vehicle door handle is activated to generate a door unlock request, the lock should actually be unlocked only if an authorized fob is located in the vehicle exterior. Otherwise, the vehicle door could be unlocked and opened by anyone outside the vehicle merely because an authorized user is present inside the vehicle. By way of another example, if a user activates a passive engine start switch inside the vehicle, the engine should actually be started only if an authorized user is present inside the vehicle.
One known method for determining the location of a fob is to employ separate vehicle antennas arranged to radiate primarily in the interior of the vehicle s and primarily in the exterior of the vehicle, respectively. In one particular type of system, the portable fob measures the received signal strength of the interrogation signals (i.e., challenge signals) from each of the respective antennas and then includes the signal strength information as part of a response message to the vehicle. The vehicle module then compares the signal strength at which the fob received the interior and exterior transmitted interrogation signals in determining whether the fob is present in the interior or exterior regions of the vehicle.
In order to properly distinguish between the interior and exterior locations, the transmission power of the interrogation signals broadcast from each of the antennas must be properly adjusted so that a fob located in the interior always receives a stronger signal from the interior antenna and so that a fob located in the exterior always receives a stronger signal from the exterior antenna. Transmission power is typically controlled by setting the gain of an amplifier that drives the respective antennas. Since the radio frequency environment of every particular model of vehicle is different due to variations in antenna location, vehicle dimensions, and the presence 20 of signal attenuating structures such as doors, windows, and vehicle trim panels, the appropriate transmission power is dependent upon the identity of the particular vehicle model. Therefore, a separate electronic module design has been required for each vehicle model so that an appropriate transmission power and radiation pattern is achieved for each unique vehicle environment. However, separate unique designs for each vehicle model result in increased cost of product development, manufacturing, and distribution.